Ohio imposes general sales and use taxes on natural gas purchases from all sellers, whether in-state or out-of-state, that do not meet its statutory definition of a "natural gas company." Ohio's state-regulated natural gas utilities (generally termed "local distribution companies" or LDC's) satisfy the statutory definition, but the State Supreme Court has determined that producers and independent marketers generally do not. LDC gas sales thus enjoy a tax exemption inapplicable to gas sales by other vendors. The very possibility of nonexempt gas sales reflects an evolutionary change in the natural gas industry's structure. Traditionally, nearly all sales of natural gas directly to consumers were by LDC's, and were therefore exempt from Ohio's sales and use taxes. As a result of congressional and regulatory developments, however, a new market structure has evolved in which consumers, including large industrial end users, may buy gas from producers and independent marketers rather than from LDC's, and pay pipelines separately for transportation. Indeed, during the tax period in question, petitioner General Motors Corporation (GMC) bought virtually all the gas for its plants from out-ofstate independent marketers, rather than from LDC's. Respondent Tax Commissioner applied the general use tax to GMC's purchases, and the State Board of Tax Appeals sustained that action. GMC argued on appeal, inter alia, that denying a tax exemption to sales by marketers but not LDC's violates the Commerce and Equal Protection Clauses. The Supreme Court of Ohio initially concluded that the tax regime does not violate the Commerce Clause because Ohio taxes natural gas sales at the same rate for both in-state and out-of-state companies that do not meet the statutory definition of "natural gas company." The court then stepped back to hold, however, that GMC lacked standing to bring a Commerce Clause challenge, and dismissed the equal protection claim as submerged in GMC's Commerce Clause argument.

Held:

1. GMC has standing to raise a Commerce Clause challenge. Cognizable injury from unconstitutional discrimination against interstate commerce does not stop at members of the class against whom a State ultimately discriminates. Customers of that class may also be injured, as in this case where the customer is liable to pay the tax and as a resultcralaw

2. Ohio's differential tax treatment of natural gas sales by public utilities and independent marketers does not violate the Commerce Clause. pp. 287-311.

(a) Congress and this Court have long recognized the value of state-regulated monopoly arrangements for gas sales and distribution directly to local consumers. See, e. g., Panhandle Eastern Pipe Line Co. v. Michigan Pub. Servo Comm'n, 341 U. S. 329. Even as congressional and regulatory developments resulted in increasing opportunity for a consumer to choose between gas sold by marketers and gas bundled with state-mandated rights and benefits as sold by LDC's, two things remained the same: Congress did nothing to limit the States' traditional autonomy to authorize and regulate local gas franchises, and those franchises continued to provide bundled gas to the vast majority of consumers who had neither the capacity to buy on the interstate market nor the resilience to forgo the reliability and protection that state regulation provided. To this day, all 50 States recognize the need to regulate utilities engaged in local gas distribution. Pp.288-297.

(b) Any notion of discrimination under the Commerce Clause assumes a comparison of substantially similar entities. When the allegedly competing entities provide different products, there is a threshold question whether the companies are indeed similarly situated for constitutional purposes. If the difference in products means that the entities serve different markets, and would continue to do so even if the supposedly discriminatory burden were removed, eliminating the burden would not serve the dormant Commerce Clause's fundamental objective of preserving a national market for competition undisturbed by preferential advantages conferred by a State upon its residents or resident competitors. Here, the LDCs' bundled product reflects the demand of a core market-typified by residential customers to whom stability of rate and supply is important-that is neither susceptible to competition by the interstate sellers nor likely to be served except by the regulated natural monopolies that have historically supplied its needs. So far as this noncompetitive market is concerned, competition would not be served by eliminating any tax differential as between sellers, and the dormant Commerce Clause has no job to do. On the other hand, eliminating the tax differential at issue might well intensify competition between LDC's and marketers for the noncaptive market of bulk buyers like GMC, which have no need for bundled protection. Thus, the question here is whether the existence of competition between marketers and LDC's in the noncaptive market requires treating the entities as alike for dor-cralaw